This PR prepares the release 1.15.1.

Summary by cubic

Prepares the axios 1.15.1 patch release by bumping version metadata and syncing the exported version. No functional or API changes.

Description

• Bump version to 1.15.1 in package.json and package-lock.json; sync lib/env/data.js exported version.
• Tidy contributors list in package.json.
• Docs: add 1.15.1 release notes and update any version badges in /docs/.
• Testing: no tests changed; none needed for a metadata-only release.

Semantic version impact

• Patch: metadata and docs-only changes; no runtime or API impact.

^{Written for commit 08d88d6. Summary will update on new commits.}